1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to an in-plane switching mode liquid crystal display device having a pattern of spacers.
2. Discussion of the Related Art
Generally, a liquid crystal display (LCD) device operates by optical anisotropy and polarization of a liquid crystal material therein. Since the liquid crystal material includes liquid crystal molecules, each having a thin and long structure, the liquid crystal material has a specific orientation according to the alignment direction of the liquid crystal molecules. Hence, the alignment direction of the liquid crystal molecules can be controlled by applying an external electric field to the liquid crystal. As the alignment of the liquid crystal molecules is changed by applying an electric field, light polarization caused by the optical anisotropy of the liquid crystal material is modulated to display image information.
One of the LCD devices widely used is a twisted nematic (TN) mode LCD device. The TN mode LCD device is configured in such a manner that an electrode is provided on each of the two substrates respectively. The direction of the liquid crystal molecules is arranged to be twisted at an angle of 90°. The TN LCD device operates such that the direction of the liquid crystal molecules is arranged by applying an electric field. However, the TN mode LCD device has a disadvantage of having a narrow viewing angle.
Therefore, various new methods have been actively developed and studied in order to solve the problem of the narrow viewing angle. An in-plane switching (IPS) mode and an optically compensated birefringence (OCB) mode are some examples of the results of the above study.
The IPS mode LCD device is configured such that two electrodes are provided on one common substrate, and liquid crystal molecules are rotated relative to the substrate with their long axes remaining substantially in parallel with the substrate. Then, an electric field is generated with respect to the substrate in parallel therewith by applying voltages between the two electrodes. That is, the major axis of the liquid crystal molecule does not rise with respect to the substrate. Therefore, since the birefringence change of the liquid crystal in the viewing direction is small, the viewing angle becomes much improved compared with that of the related art TN mode LCD device.
FIG. 1 is a plan view of a part of a lower substrate of an IPS mode LCD device.
Referring to FIG. 1, the lower substrate includes a plurality of gate lines 13 and common lines 54 substantially in parallel with each other and a plurality of data lines 15 substantially perpendicular to the gate lines 13 and common lines 54.
Pixels 10 are defined in the lower substrate as the region surrounded by the gate lines 13, the common lines 54, and the data lines 15, 15′.
Further, a gate electrode 31 is formed at one side of the gate line 13, and a source electrode 33 is formed at one side of the data line 15 adjacent to the gate electrode 31 and partially overlapping the gate electrode 31. A drain electrode 35 is formed to face the source electrode 33 and is space from the source electrode 33 by an interval. Together, the gate electrode 31, the source electrode 33 and the drain electrode 35 form a thin film transistor region (T).
Further, the common line 54 has a plurality of common electrodes 54a extending therefrom. The drain electrode 35 is connected to a lead interconnection line 37 from which pixel electrodes 37a extend. The common electrode 54a and the pixel electrode 37a are formed in an alternating manner. An image display region of the pixel 10 is formed by the plurality of the common electrodes 54a and the pixel electrodes 37a. 
A common voltage input from the common lines 54 is applied to the common electrodes 54a formed in the pixel 10. Various levels of image signals are applied to the subpixel via the data line 15 when a gate voltage is applied via the gate line and gate electrode.
Therefore, a plane electric field is formed by the voltage applied to the pixel electrode 37a and the common electrode 54a, and the alignment degree of the liquid crystal molecules can be varied depending on the intensity of such electric field so as to display images.
A block 39 refers to a region in which images are displayed by the pixel electrode 37a and the common electrode 54a according to the applied plane electric field. Each pixel 10 includes a plurality of the blocks 39. As illustrated in FIG. 1, a four-block type in which four blocks 39 are formed in one pixel 10 is widely used.
FIG. 2 is a sectional view of a related art in-plane switching mode LCD device taken along the line I-I′ of FIG. 1.
Referring to FIG. 2, the related art in-plane switching mode LCD device is configured such that a black matrix 8 and a color filter 6 are formed on an upper substrate 5. A lower substrate 22 is provided with the pixels 10 as illustrated in FIG. 1 arranged in a matrix. In addition, the liquid crystal 20 as described above is in a predetermined gap between the upper substrate 5 and the lower substrate 22, and the two substrates are sealed by a sealant (not shown) deposited on the edges of the substrates.
Further, spacers (not shown) are disposed between the upper substrate 5 and the lower substrate 22 to maintain the predetermined gap between the substrates 5 and 22 so that the liquid crystal 20 can be injected therebetween or applied by dispensing.
Light does not penetrate the LCD device as illustrated in FIGS. 1 and 2 except in the image display regions of the pixel 10, i.e., the four blocks 39. Therefore, penetration of unnecessary light is shielded in the region except for the four blocks 39 where the region corresponds to the black matrix 8 of the upper substrate 5.
However, because the data lines 15, 15′ and the common electrodes 54a, 54a′ adjacent to the data lines 15, 15′ are not included in the blocks 39, they are shadowed by the black matrix 8, as illustrated in FIG. 2. Accordingly, even though the data lines 15, 15′ and the common electrodes 54a, 54a′ are shielded by the black matrix 8, light leakage can occur where there is misalignment of the upper and lower substrates 5, 22 during manufacturing.
Particularly, as the substrate size becomes large, a misalignment of the upper and lower substrates 5, 22 becomes more serious. Therefore, it may be necessary to widen the width of the black matrix 8 of the upper substrate 5 sufficient to cover a part of the blocks 39, as illustrated in FIG. 2, which results in the decrease of the final aperture ratio.
Further, as illustrated in FIG. 2, even though the width of the black matrix 8 is widened, the light leakage may also occur due to the refraction of light in that region.
Before the explanation of an in-plane switching mode LCD device of the present invention, a spacer formed between an upper substrate and a lower substrate is explained to maintain a space therebetween.
The spacer is distributed between the upper and lower substrates to maintain a cell gap uniform, and there are various types of spacers, such as a fiber-shaped spacer, an elastic ball-shaped spacer, or an adhesive spacer.
However, since the spacer particles are dispersed on the substrate randomly, the spacer is sometimes found to exist inside an effective pixel region, which causes a problem in that the spacer is seen, or incident light is scattered thereby decreasing the contrast of a liquid crystal panel.
Therefore, a method has been introduced for forming the spacer by using a photolithography process to solve the above problem. The method is performed by depositing a photoresist layer on the substrate, and illuminating ultraviolet rays through a mask before developing the substrate to form a dot or stripe-shaped spacer. The spacer is formed in a region other than an effective pixel region, and the cell gap can be controlling by the thickness of the photoresist layer, which provides advantages of controlling the width of the cell gap easily and increasing the precision.
As described above, spots may be seen on the image display of the related art in-plane switching mode LCD device due to light leakage.